Cellulose ester manufacture and composition therefor



G. A; RICHTER Dec. 59 H933.

CELLULOSE ESTER MANUFACTURE AND COMPOSITION THEREFOR Filed Sept. 23,1930 QN s sin s ffiwfff MWA/if' /ff /fww @if Patented Dec. 5, 1933UNITED STATES PATENT OFFICE CELLULO SE E STER MANUFACTURE ANDCOMPOSITEON THEREFOR of Maine Application September 23, 1930 Serial No.483,790

13 Claims.

This invention relates to cellulose ester manufacture and tocompositions ci cellulose ber more particularly intended for conversioninto cellulose esters, such as nitrate and Xanthate.

In the preparation of some cellulose esters, such as the nitrate orXanthate, it is desirable that the cellulose fiber used as the rawmaterial be of low solution viscosity, by which it is meant that theesters preparable therefrom, when treated with suitable solvent medium,form solutions of low viscosity. There are various methods of reducingthe solution viscosity ot cellulose fiber, but some of the best ones, inthe sense that they reduce the solution viscosity oi the ber drastical-15 ly, cause serious physical and chemical injury to the iber, Forinstance, a sharp reduction of the solution viscosity of cellulose fibermay be effected by treating the iiber with a solution oi acid, such ashydrochloric or sulphuric, or solutions of oxidizing agents, such as4hypochlorite or permanganate, but in such cases the fiber may suffer adrastic cut in its alpha cellulose content and a transformation into apowdery condition. The resulting iiber while convertible into celluloseesters, such as nitrate or Xanthate, capable of forming solutions of lowviscosity, nevertheless is apt to be unsatisfactory from that standpointthat articial Silks, iilms or lacduers produced from such solutionshave. poor physical properties. Again, the powdery fiber cannot becondi-- tioned to advantage for conversion into esters. For instance,its shredding is accompanied by the generation of much dust; itsformation into thick sheets results in products of high density throughwhich converting chemicals can penetrate only with difliculty. Suchsheets are so fragile, moreover, that they break easily; and thin sheetsor papers are even more lacking in tenacity, strength, and tearresistance.

I have discovered that it is distinctly advantageous to blend celluloseber of one solution viscosity with cellulose ber of lower solutionviscosity, especially when the liber of lower solution viscosity hasbeen physically and chemically degraded by previous treatment in theattainment of the low solution viscosity characteristic. One of theimportant advantages of such blending resides in the fact that theproduct has a solution viscosity much lower than the calculated averageor mean value of its components, based on their solution viscosity andtheir. proportions. For instance, a blend or mixture comprising of eachcomponent has a solution viscosity far less than the arithmetic mean oraverage solution viscosity of the two components. An important advantageof such blending is that the ber of higher solution viscosity, beingphysically unde- .graded makes possible the sheeting ofthe blend intoboards or papers which are not so dense or crumbly to give rise todiiiiculties upon consequent conversion into esters. About 28% to 50% oflong fiber of higher solution viscosity, based on the blend, forinstance, the unhydrolyzed iiber hereinafter mentioned having a solutionviscosity of about 5, is usually ample to permit the formation ofsatisfactory boards or sheets from the blend on machinery of thepapermaking type. It is of course possible to use fibers of highersolution viscosity for this purpose, as such fibers possess therequisite physical and chemical characteristics.

There are various ways of applying the principles of the presentinvention, using various kinds of oers of one solution viscosity and oflower solution viscosity. For instance, the fiber of lower solutionviscosity may be of wood origin, whereas the ber of higher solutionviscosity may be relatively long, such as cotton or linen, particularlywhen the blend is to be formed into thick sheets or papers having goodstrength and tear resistance characteristics. If desired, the fiber oflower solution viscosity may be produced as by causing hydrolysis ofcellulose liber through the action of comparatively dilute or mild acidsolutions at elevated temperature, and, if desired,l under pressure, orthrough the action of comparatively concentrated or strong acid solutionat low temperature, for instance, room temperature. The ber subjected tohydrolysis may be one which has previously been mercerized, asmercerized fiber lends itself to relatively facile lowering. of itssolution viscosity by hydrolysis, The ber of higher solution viscositymay be in mercerized or in unmercerized condition, although whennitrocellulose is to be the ester prepared from the blend, it may bepreferable to use a mercerized liber as the component of higher solutionviscosity, because of the higher grade nitrocellulose obtainabletherefrom. The ber of higher solution viscosity may be one which, too,has undergone some hydrolysis or other solutionviscosity-loweringtreatment short of eifecting injury to the ber or of reducing itssolution viscosity to a value anywhere nearly as low as that of thecomponent of low solution viscosity. It is, ofcourse, possible to usebers of low solution viscosity produced by the use of oxidizing or otheragents.v In fact, my blend may comprise more than two components ofdiiferent solution viscosities and of -diiferent origins. The blend may-through an orifice of standard size.

be in bulk form, as when shredded, or in the form of thick sheets orpapers. The component of higher solution viscosity may be in mercerizedcondition to advantage in the case of a bulk blend to be converted assuch into esters, but when sheets or papers are to be made from theblend, it may be desirable to beat or hydrate the component of highersolution viscosity, in which case it is preierably in unmercerizedcondition to permit such hydration. viscosity may be hydrated separatelyin the beater engine and the component of lower solution viscosity thenadded thereto, or the blend as a whole may be beaten prior to deliveryto the paper-making machines. In any event, the ber of higher solutionviscosity imparts strength and tear resistance to the resulting sheetsor papers formed from the blend; and the fiber of lower solutionviscosity, when degraded to the point of being of short length andpowders, serves as an excellent ller in the sheets or papers.

The solution viscosity of the resulting blend may be as high as from 4to 10, especially in those cases where a fiber of high solutionviscosity and high strength has been blended in substantial amount witha ber of low solution viscosity. A blend of this type having a solutionviscosity of, say 6, when converted into soda cellulose and subjected tocomparatively mild ageing, may be xanthatable into viscose syrup fromwhich rayons and lms of excellent characteristics may be produced. Onthe other hand, blends having a solution viscosity below 1 may beproduced by blending as much as 50% or more of a cellulose liber havinga solution viscosity of say, about 5, with hydrolyzed fiber of very lowsolution viscosity.

On the accompanying drawing, I have shown two curves illustrating theeiect on solution viscosity of blending unhydrolyzed fibers of solutionviscosities of about 5 with hydrolyzed bers of a solution viscosity ofabout 0.3. The dark curve represents what happens to the solutionviscosity when an unhydrolyzed iiber is blended with a hydrolyzed ber,and the light curve represents what happens to the solution viscositywhen similar unhydrolyzed but mercerized ber is blended with similarhydrolyzed ber. It is to be observed that in a blend comprising 50% eachof the two components, rather than obtaining a mean or average value ofthe solution viscosities of the two components amounting to about 2.0,it is found that a solution viscosity below 0.5 is realized. The beremployed as raw material in ascertaining the solution viscosities valuesdepicted by the curves, was a white wood liber of high alpha-cellulosecontent, but such fiber is more or less representative of what takesplace in the case of ilbers of other origins.

The term solution viscosity as herein applied to cellulose fiber is anarbitrary one, being indicative of the viscosity of a cellulose estersolution preparable therefrom. The usually employed as a standard is acuprammonium cellulose solution of prescribed cellulose concentration,the viscosity being determined by measuring the time of efflux of adenite volume of such solution under standard conditions, The solutionviscosity of iberr is herein given in absolute c. g. s. units, and isdetermined by measuring the viscosity of a solution of 6 grams of fiberin a cuprammonium cellulose solution composed of 225` cc. of 28% ammoniawater containing 9 grams of cuprous oxide. The c. g. s.unit

The component of higher solution.

solution is employed because it is definite, denoting a viscosity 100times that of water at 20 C., wherefore a cuprammonium cellulosesolution of standard composition identifying a ber as having a solutionviscosity of 10 is 1000 times as viscous as water at 20 C. Glycerine,which is often referred to when dealing with the solution viscosity ofcellulose liber, for example, has a value of between 8 and 10 units.

What I claim is:

1. A process which comprises hydrolyzing cellulose fiber to lower itssolution Viscosity to below 1, blending the hydrolyzed fiber with about20% to 50%, based on the weight of the blend, of substantiallyunhydrolyzed cellulose liber, and converting the blend into celluloseesters.

2. A process which comprises treating cellulose fiber with an oxidizingagent to lower the solution viscosity of such fiber to below 1, blendingthe resulting product with about 20% to 50%, based on the weight of theblend, of cellulose ber having a solution viscosity of at least about 5and converting the resulting blend into cellulose esters.

3. A cellulose product whose solution viscosity is less than 1 andconsisting of a blend of hydrolyzed cellulose ber of a solutionviscosity below l and about 20% to 50%, based on the weight of theblend, of substantially unhydrolyzed cellulose iiber of a solutionviscosity of at least about 5.

4. A cellulose product whose solution viscosity is less than 1 andconsisting of a blend of an oxidized cellulose ber of a solutionviscosity below l and about 20% to 50%, based on the weight of theblend, of comparatively non-oxidized cellulose fiber of a Vsolutionviscosity of at least about 5.

5. A cellulose product whose solution viscosity is less than 1 andconsisting of a blend of a crumbly cellulose ber of a solution viscositybelow 1 and about 20% to 50%, based on the weight of the blend, of muchstronger cellulose fiber of a solution viscosity of at least about 5.

6. A cellulose product whose solution viscosity is less than 1 andconsisting of a blend of cellulose ber of a solution viscosity below 1and about 20% to 50%, based on the weight of the blend, of mercerizedcellulose fiber of a solutionV viscosity of at least about 5.

'7. A cellulose product .whose solution viscosity is less than 1 andconsisting of a blend of hydrolyzed ber of a solution viscosity below 1and about 20% to 50%, based on the weight of the blend, of mercerizedcellulose ber of a solution viscosity of at least about 5.

8. A cellulose product whose solution viscosity is less than l andconsisting of a blend of cellulose ber of a solution viscosity less than1 and about 20% to 50%, based on the weight of the blend, of celluloseber of a solution viscosity of at least about 5.

9. A cellulose sheet whose solution viscosity is less than 1 andconsisting of a blend of powdery cellulose fiber of a solution Viscositybelow 1 and about 20% to 50%, based on the weight of the blend, of muchstronger cellulose fiber of a solution viscosity of at least about 5.

10. A cellulose sheet whose solution viscosity is less than l andconsisting of a blend of comparatively weak wood iibers of a solutionviscosity below 1 and about 20% to 50%, based on the weight of theblend, of longer fibers of a solution viscosity of at least about 5.

product with about 20% to 50%, based on the weight of the blend, of berof a solution viscosity of at least about 5, and converting the blendinto cellulose esters.

13. A product consisting of a blend of cellulose ber Whose solutionviscosity is at least about 5 and about 50% by weight of cellulose fiberwhose solution viscosity is less than 0.5.

GEORGE A. RICHTER.

